When you’re trying to establish a long suit in a suit contract, it’s often best to ruff low cards first rather than cash high ones. Here’s a case in point where East is dealing, with East-West vulnerable:

                             NORTH
                            ♠️ A Q 10 3
                            ♥️A 8
                            ♦️ A J 8 7 5 3
                           ♣️ K

WEST                                               EAST
♠️ 9 8 7 2                                       ♠️ J
♥️ K 10 9 5 3                                 ♥️ Q 4 2
♦️Q 10                                           ♦️ 9 6 4 2
♣️ 9 3                                             ♣️ J 8 6 5 4

                         SOUTH
                        ♠️ K 6 5 4
                        ♥️J 7 6
                        ♦️ K
                        ♣️ A Q 10 7 2

The bidding proceeded as follows:

East          South           West           North
Pass          1♣️             Pass            1♦️
Pass          1♠️             Pass           4NT
Pass          5♥️•            Pass          6♣️
Pass          6♠️             All Pass

• Two of the five key cards (four aces, trump king)

Opening lead: ♣️9

At some point declarer cashed the ♦️K, the ♦️A and the ♦️J. Unfortunately, that set up the ♦️9, which proved fatal. Do you see what could have been done differently?

After cashing the ♦️A and ♦️K, declarer should have led a low diamond for a ruff. Now the suit sets up.

Declarer also could have tried to  set up the club suit: ♣️K, ♣️A, low club for a ruff. In this case, the suit doesn’t completely set up.

Better to establish the longer suit.